#3 gatoraid is especially useful after #4
I got a new mousepad for my d3 marathon that has this awesome little pad at the bottom for wrist support. Also have some saline solution handy, my eyes tend to get bloodshot and dry after playing games for long periods of time.
Unlike some of you i will not be playing at a desk, my first D3 experience will be on my laptop so I've set up the couch as a temp game station. I have a nice sturdy pillow with a legal pad to place my mousepad/mouse on, it gives my arm a place to rest and it very very comfortable and doesn't limit movement at all. I have a usb cooling pad for my laptop with a non-slip surface, keeps it nice and cool and steady as i smash keys :). Kitchen is about 10 steps away and the bathroom is about 15 steps. MY BODY IS READY, the location is set up, all i need now is the game!